1. Field of the Invention
The present invention relates to a draft vehicle system, and particularly to a draft vehicle system for a radiation imaging inspection system.
2. Description of the Related Art
With the increasingly wide application of large containerized cargo inspection systems, it has been more and more concerned whether a vehicle under inspection can pass through a scanning passage quickly and safely during inspection since the quick and safe passing of the vehicle is a key factor to vehicle passing rate and application of the system. Conventionally, special traction devices for the inspection systems comprise a flat car, a plate conveyer, small traction vehicles, and the like.
For example, an inspection system has an inspection passage of a length of 60 m and two portions located outside respective ends of the inspection passage and each having a length of 40 m. A traction system for the inspection system is very huge so that the system occupies a large area for civil construction. Further, it is high in cost for manufacturing and mounting components of the system, and is difficult in maintenance. In addition, the system can not randomly be used for inspection at a place different from a spot where the system is located.
Another existing inspection system is configured to have three underground traction vehicles for cycle traction. However, action of the traction vehicles between the ground and the underground makes the system complicated. In addition, when the traction vehicle draws a container car, front wheel of the container car may slip, so that the container car probably drops forwards or rearwards from the traction vehicle to impact and damage the container car and the inspection system.
Chinese Patent Application CN 1324751 A filed by the present applicant discloses an automatic flat car for a stationary container inspection system. In inspection, a vehicle under inspection completely moves onto the automatic flat car. The flat car is equipped with longitudinal and transverse travel mechanisms so that it can moves on a rectangular rail to cycle or reciprocate. The flat car transports vehicles under inspection to pass through a scanning passage. In order to ensure passing rate of vehicles under inspection in the system, one system is generally provided with one or a plurality of automatic flat cars. The automatic flat car bears whole weight (including cargo) of a vehicle under inspection. Due to this, it is huge, complicated in structure, excessive in number of attachments, large in consumption of energy, great in occupied area, and high in manufacturing cost and maintenance cost.
Chinese Patent Application CN 1324750 A filed by the present applicant discloses a plate link chain conveyor for a stationary container inspection system. The conveyor comprises a driving device, a front driving wheel device, a frame, a rear tensioner, and the like. The conveyor is suitable for transporting containers or pelletized cargo, but is inapplicable to traction of trucks under inspection and especially a container lorry with cargo.
Chinese Patent Application CN 1607135A filed by the present applicant discloses a draft vehicle of a draft vehicle system for radiation imaging. A driving device for the draft vehicle includes winches disposed at both ends of an inspection passage, respectively. The winches draw the draft vehicle to pass through the inspection passage by means of steel cable. In inspection, the draft vehicle is locked, and front wheels of a vehicle under inspection move onto the draft vehicle and stop at positioning sockets of the draft vehicle to be positioned. However, the positioning sockets can only abut against the wheels from rear sides of the wheels when the draft vehicle moves, but can not prevent the vehicle under inspection from swinging back and forth because of inertia force generated by starting and stopping the draft vehicle. In addition, in inspection, if rails for the draft vehicle are slightly uneven, speed of the draft vehicle and the vehicle under inspection varies. A design height of the draft vehicle will affect usage of the draft vehicle to a great extent because of limitations of structure. When a container lorry moves onto or leaves the draft vehicle, the draft vehicle sometimes scratches parts of the container lorry such as a chassis and an oil tank to harm the container lorry under inspection. Moreover, when the winch drives the draft vehicle to start and stop, it generates a great impact on the steel cable so that the speed of the vehicle under inspection varies. As a result, image quality is adversely affected. Therefore, a radiation inspection system to which the draft vehicle is applied is poor in reliability, the image quality of the image obtained by the system is unstable, and the system requires high-quality civil construction.
Therefore, the conventional inspection systems has a huge traction system, is complicated in structure, excessive in appurtenant facilities, and large in energy consumption.